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Preclinical targeted alpha therapy for subcutaneous melanoma.

An alpha-emitting immunoconjugate (AIC) against malignant melanoma was prepared from the radioisotope bismuth-213 and a melanoma monoclonal antibody, and was used to control the growth of subcutaneous melanoma in a nude mouse model. Activity tolerances were found to be 8 mCi/kg for intraperitoneal injection of the conjugate, and 10 mCi/kg for intralesional injections. Local targeted alpha therapy (TAT) via intralesional injections of activities in the range 12.5-200 microCi shows a very high level of inhibition of tumorigenesis and regression of tumours. Results show that isolated cancer cells and preangiogenic cell clusters can be eliminated by local TAT, and that intralesional injections of 100 microCi of AIC are sufficient to cause complete regression of melanomas with volumes up to 300 mm3 without any observed side effects. Systemic TAT was less effective, with all tumours experiencing growth delay and limited inhibition of tumour growth. These data provide the basis for clinical trials of TAT in recurrent subcutaneous melanoma.

Animals↗

Vaccination of mice with lipopolysaccharide (LPS) and LPS-derived immuno-conjugates from Leptospira interrogans.

Mice were vaccinated with lipopolysaccharide (LPS) from Leptospira interrogans serovar pomona or hardjo, or with the polysaccharide (PS) fraction of the LPS, or with an immunoconjugate of PS and diphtheria toxoid (DT). Maximum agglutinin titres were found 6-10 weeks after vaccination with LPS or PS-DT conjugate; the latter elicited antibody titres at least 10 times higher than those produced in response to LPS. Animals failed to react significantly to PS. Titres elicited by antigens of serovar pomona were higher than those elicited by serovar hardjo.

Animals↗

Anti-phosphatidylcholine antibodies in patients with brucellosis.

An indirect ELISA was adapted to measure individual classes of anti-phosphatidylcholine (PC) antibodies in patients with brucellosis; a comparison was made with patients with other infectious diseases and healthy human controls. Immunoconjugates of alpha, gamma or mu chain specificity were used. The results were compared with those of conventional tests for brucella antibodies, Rose Bengal, microagglutination (MAT) and Coombs tests, as well as with VDRL. The results indicated that although all sera from patients with brucellosis were VDRL negative, 97% of them (30 of 31) had higher levels of IgA or IgG anti-PC antibodies than the healthy control group. The IgM anti-PC antibodies isotype was not discriminatory between both groups. Seven sera (19%) from patients with other infections had values of IgG anti-PC higher than those of the healthy group; three of them were VDRL positive. The mean ELISA values of IgG and IgA anti-PC (serum diluted 1 in 1600) in the brucellosis and healthy groups were: IgG, 0.80 SEM 0.17 versus 0.23 SEM 0.10; and IgA, 0.86 SEM 0.26 versus 0.35 SEM 0.15. The sensitivity and specificity for the ELISA-PC were: IgG, 96.8% and 96.5%, respectively; IgA, 90.3% and 89.7%, respectively. Only one of 14 individuals clinically cured from brucellosis had significant IgG anti-PC antibodies. In contrast, all of these patients gave positive values in the conventional test for brucellosis. No correlation was found between the serum levels of IgA, IgG anti-PC by ELISA-PC and the results of the MAT or Coombs tests.

Agglutination Tests↗

A monoclonal antibody, KM10 reactive with human gastrointestinal cancer and its application for immunotherapy.

A monoclonal antibody, KM10 (IgG1) was produced by fusing spleen cells from a human gastric cancer cell (MKN45)-primed BALB/c mouse with the murine myeloma cell line X63-Ag8-653. The antibody reacted strongly with the plasma membrane of human gastrointestinal carcinoma. Sections of the malignant and benign tissues were tested with immunoperoxidase. All of 10 (100%) large intestinal cancers, 26 of 31 (84%) gastric cancers, 5 of 7 (71%) pancreatic cancers and all of 3 (100%) ampullary cancers reacted positively. Moderate or weak reactivity was observed with normal human tissues, hepatoma and carcinomas of mammary, thyroid and adrenal glands. According to a study of the distribution of 125I-labeled KM10 in nude mice bearing human gastric cancer, KM10 selectively localized in tumor tissue rather than normal tissue. Whole body autoradiography also supported such a selective distribution. Destruction of antigenic properties by pronase digestion demonstrated its protein nature and by Western blot analysis, it was identified as a protein with an Mr of 180-200 kd. KM10-adriamycin (ADM) conjugate was prepared via an oxidized dextran bridge and this immunoconjugate retained the binding activity against human gastric cancer. MKN45 cells were inoculated subcutaneously into athymic mice and intravenous treatment was begun when the tumor became measurable. A dose-dependent antitumor activity was observed in vivo with KM10-ADM conjugate, while this conjugate was less toxic than free ADM.

Animals↗

Therapeutic effect of ansamitocin targeted to tumor by a bispecific monoclonal antibody.

We have constructed a murine hybrid hybridoma that secretes a bispecific monoclonal antibody (mAb) by fusing a hybridoma secreting an anti-ansamitocins mAb with a hybridoma secreting an anti-human transferrin receptor (TfR) mAb that binds to human A431 epidermoid carcinoma cells. The bispecific mAb, reactive to both ansamitocins and TfR, was purified by a combination of hydrophobic column chromatography and hydroxyapatite high-performance liquid chromatography, and evaluated in in vivo experiments using human tumor cell-implanted nude mice. Ansamitocin P-3 targeted through one of the antigen combining sites of the bispecific mAb was potentially more effective in suppressing the growth of established A431 tumor xenografts implanted on nude mice than unconjugated ansamitocin P-3 or the immunoconjugate of ansamitocin P-3 and monospecific anti-ansamitocins antibody, and the targeted ansamitocin P-3 finally eradicated the tumor mass. The bispecific mAb also played an important role in reducing such undesirable side-effects of ansamitocin P-3 as the loss of body weight, the damage to liver functions and the decrease in the number of white blood cells.

Animals↗

The role of gemtuzumab ozogamicin in acute leukaemia therapy.

Gemtuzumab ozogamicin (GO) is an immunoconjugate that binds to CD33 on the surface of acute myeloid leukaemia (AML) blasts and, after internalisation, releases a cytotoxic drug, calicheamicin. GO is approved by the US Food and Drug Administration for the treatment of CD33-positive AML at first relapse in patients 60 years and older who are not candidates for other cytotoxic therapy. GO as a single agent has low antileukaemic activity. When given to patients meeting the criteria noted above, it produces a complete response (CR) rate of only 12%, with another 12% achieving CR with inadequate platelet recovery (CRp). The median survival of patients treated with GO monotherapy is 11.2 months. GO therapy at 9 mg/m(2) is complicated with hepatic veno-occlusive disease in 5-10% of patients, particularly prior to or following stem cell transplantation. GO at lower doses combined with chemotherapy as induction or postremission therapy is promising, however, and phase III trials are ongoing. GO is probably most active in acute promyelocytic leukaemia (APL). It is used for induction regimens in high-risk APL and for the elimination of minimal residual APL. Case reports suggest that GO also has activity in CD33-positive acute lymphoblastic leukaemia. In conclusion, single agent GO can induce responses in patients with CD33-positive AML in first recurrence. The future of GO is its use in combination with other cytotoxic agents. Ongoing clinical trials may better define the role of GO combinations, particularly in untreated AML.

Acute Disease↗

A dominant linear B-cell epitope of ricin A-chain is the target of a neutralizing antibody response in Hodgkin's lymphoma patients treated with an anti-CD25 immunotoxin.

Hodgkin's lymphoma patients treated with an anti-CD25 Ricin toxin A-chain (RTA)-based Immunotoxin (RFT5.dgA) develop an immune response against the toxic moiety of the immunoconjugate. The anti-RTA antibody response of 15 patients showing different clinical features and receiving different total amounts of RFT5.dgA was therefore studied in detail, considering antibody titre, IgG and IgM content, average binding efficacy and ability to inhibit in vitro the cytotoxicity of a RTA-based Immunotoxin. No correlations were found between these parameters and the clinical features of the patients or the total amount of Immunotoxin administered. However, using a peptide scan approach we have identified a continuous epitope recognized by all patients studied, located within the stretch L161-I175 of the RTA primary sequence, close to a previously identified T-cell epitope. The ability of anti-L161-I175 antibodies to recognize folded RTA and to affect the biological activity of RTA by inhibiting RTA-IT cytotoxicity in vitro revealed that they may exert an important role in IT neutralization in vivo. Discovery of RTA immunodominant epitopes which are the target of anti-RTA immune response may lead to the development of immunomodulating strategies and to more successful treatment schedules.

Antibodies↗

Synthesis of a new class of isothiocyanatopeptide bifunctional chelating agents for coupling to monoclonal antibodies.

The preparation of a new class of isothiocyanatopeptide bifunctional chelating agents, Boc-glycyl-L-(p-NCS)phenylalanylglycylglycine ethyl ester 1, N-(S-acetylmercaptoacetyl)-L-(p-NCS)phenylalanylglycylglycine ethyl ester 2, and N-(S-acetylmercaptoacetyl)glycyl-L-(p-NCS)phenylalanylglycine ethyl ester 3, starting from Boc-L-(p-nitro)phenylalanine 5 is described. The key intermediates, nitropeptides 7, 8 and 12, were prepared by standard DCC coupling and a deprotection procedure. The nitropeptides 7 and 12 on condensation with N-succinimidyl-S-acetylthioacetate provided a good yield of the corresponding S-(acetylmercaptoacetyl)nitropeptides 10 and 13, respectively. Catalytic hydrogenolysis of compounds 8, 10 and 13, followed by thiophosgenyation gave 28-95% yield of target products 1, 2 and 3, respectively. Compounds 1-3 were conjugated to the monoclonal antibody D612 reactive with human colon carcinoma using 12/1 to 60/1 ligand to antibody molar ratios, and the conjugates were labeled with 99mTc. The in vitro cell binding results of these immunoconjugates demonstrate that they retained their antibody binding specificity.

Antibodies, Monoclonal↗

Pulchellin, a highly toxic type 2 ribosome-inactivating protein from Abrus pulchellus. Cloning heterologous expression of A-chain and structural studies.

Pulchellin is a type 2 ribosome-inactivating protein isolated from seeds of the Abrus pulchellus tenuiflorus plant. This study aims to obtain active and homogeneous protein for structural and biological studies that will clarify the functional aspects of this toxin. The DNA fragment encoding pulchellin A-chain was cloned and inserted into pGEX-5X to express the recombinant pulchellin A-chain (rPAC) as a fusion protein in Escherichia coli. The deduced amino acid sequence analyses of the rPAC presented a high sequential identity (> 86%) with the A-chain of abrin-c. The ability of the rPAC to depurinate rRNA in yeast ribosome was also demonstrated in vitro. In order to validate the toxic activity we promoted the in vitro association of the rPAC with the recombinant pulchellin binding chain (rPBC). Both chains were incubated in the presence of a reduced/oxidized system, yielding an active heterodimer (rPAB). The rPAB showed an apparent molecular mass of approximately 60 kDa, similar to the native pulchellin. The toxic activities of the rPAB and native pulchellin were compared by intraperitoneal injection of different dilutions into mice. The rPAB was able to kill 50% of the tested mice with doses of 45 microg x kg(-1). Our results indicated that the heterodimer showed toxic activity and a conformational pattern similar to pulchellin. In addition, rPAC produced in this heterologous system might be useful for the preparation of immunoconjugates with potential as a therapeutic agent.

Abrus↗

Interleukin-2 fusion toxin: targeted therapy for cutaneous T cell lymphoma.

The interleukin (IL)-2 receptor has proved an attractive target for T cell-directed therapies. Agents including monoclonal antibodies, single-chain antibody immunoconjugates, radioimmunoconjugates, and, most recently, ligand fusion toxins have demonstrated activity in vitro and in clinical trials in both hematologic malignancies and diseases characterized by proliferation of activated T cells, such as graft-versus-host disease. DAB389IL-2 (ONTAK) is a ligand fusion toxin consisting of the full-length sequence of the IL-2 gene genetically fused to the enzymatically active and translocating domains of diphtheria toxin. DAB389IL-2 and its predecessor, DAB486IL-2, have demonstrated activity in a variety of diseases, including cutaneous T cell lymphoma (CTCL), psoriasis, rheumatoid arthritis, and HIV infection. Further clinical development of IL-2 fusion toxins in CTCL and other hematopoietic malignancies is predicated on identification of the high-affinity IL-2 receptor complex on the malignant cells and on a better understanding of the biological determinants of cytotoxicity of these molecules in vivo.

Antineoplastic Agents↗

Leukemic gingival infiltrate as an indicator of chemotherapeutic failure following monoclonal antibody therapy: a case report.

Treatment options are limited for patients with relapsed acute myelogenous leukemia (AML), particularly when the disease is refractory to standard cytotoxic chemotherapy. Targeted drug therapy offers the advantage of delivering higher doses of non-cross resistant chemotherapy with potentially less systemic toxicity. Gemtuzumab ozogamicin (Mylotarg, Wyeth-Ayerst Laboratories) is an immunoconjugate that consists of humanized anti-CD 33 antibody linked to the potent anti-tumor antibiotic calicheamicin and has been an effective therapy for some patients with relapsed AML. However, the overall utility of gemtuzumab ozogamicin is not well defined. For instance, it is not known how well this antibody will target extramedullary disease. This article reports gemtuzumab treatment of refractory AML in a 32-year-old man. At the time of recurrence, his bone marrow was hypoplastic and without leukemia, but the condition progressed resulting in marked leukemic infiltration of the oral mucosa. This case history raises the possibility that leukemic sanctuary sites may exist, and that monoclonal antibody therapy may have sub-optimal activity in non-medullary sites of disease.

Adult↗

Experimental radioimmunotherapy.

Radiolabeled monoclonal antibodies have been used for radioimmunotherapy studies with human tumor spheroids and murine and human tumor xenografts in experimental animals. This paper reviews the work that has been performed in these models with different types of cancer, and highlights those papers that have presented dosimetry estimates and attempts to correlate the findings. Radioimmunotherapy studies in multicell spheroids, as a model for micrometastases, have been performed in human neuroblastoma, colon cancer, and melanoma cell lines using 131I-, 125I-, 186Re-, and 212Bi-labeled antibodies. The uniform geometry of the spheroid has allowed radiation dose estimates to be made. Up to three logs of cell kill have been achieved with 131I- and 186Re-specific antibody with minimal toxicity from labeled nonspecific antibody, but 212Bi-antibody had little effect because of its short half-life as shown by Langmuir. It appears that the two most important factors for therapeutic efficacy in this model are good penetration of the radiolabeled antibody and an adequate radionuclide half-life to allow penetration of the immunoconjugate prior to significant radionuclide decay. Radioimmunotherapy studies in animals bearing transplants of colon cancer, leukemia, lymphoma, hepatoma, renal cell carcinoma, neuroblastoma, glioma, mammary carcinoma, small cell lung carcinoma, cervical carcinoma, ovarian carcinoma, and bladder cancer have been performed with 131I, 90Y, 186Re, 153Sm, and 177Lu beta emitting, and 212Bi alpha emitting radionuclides conjugated to monoclonal antibodies. A few studies compared different radionuclides in the same model system. The approaches that have been used in these studies to estimate tumor dosimetry include the MIRD approach, thermoluminescent dosimetry, autoradiography, and comparison to external irradiation. The majority of investigators have estimated the dose to tumor and normal organs using MIRD-based calculations (time-activity curve and equilibrium dose constant method). The range of tumor doses has been between 17 and 11 171 mGy/MBq of administered radioactivity. The effectiveness of radiolabeled monoclonal antibody therapy depends on a number of factors relating to the antibody such as specificity, affinity, and immunoreactivity. The density, location, and heterogeneity of expression of tumor-associated antigen within tumors will affect the localization and therapeutic efficacy of radiolabeled antibodies, as will physiological factors such as the tumor vascularity, blood flow, and permeability. These factors are discussed and examples are presented.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

Antimyosin-labeled monocrystalline iron oxide allows detection of myocardial infarct: MR antibody imaging.

The synthesis and in vivo antigen targeting of a novel iron oxide compound were studied. A monocrystalline iron oxide nanoparticle (MION) was synthesized that contains a small (mean diameter, 2.9 nm +/- 0.9) single crystal core, passes through capillary membranes, and exhibits superparamagnetism. The MION was attached to antimyosin Fab (R11D10) and used for immunospecific magnetic resonance (MR) imaging of cardiac infarcts One hour after intravenous administration of MION-R11D10 in rats (100 mumol/kg), a marked decrease in the signal intensity of infarcted myocardium was observed. Immunohistochemical correlation confirmed the specific binding of the immunoconjugate to infarcted, but not to normal, myocardium. No decrease in cardiac signal intensity was observed when unconjugated MION was administered intravenously. The results indicate the feasibility of immunospecific MR imaging in living organisms.

Animals↗

Immunoscintigraphy performed with In-111-labeled CYT-103 in the management of colorectal cancer: comparison with CT.

Immunoscintigraphy performed after intravenous administration of indium-111-labeled CYT-103, an immunoconjugate of monoclonal antibody B72.3, was evaluated in patients with suspected primary or recurrent colorectal cancer at 25 centers in the United States. Gamma camera imaging, computed tomography (CT), and confirmatory surgical exploration were completed in 169 of 227 patients who received single infusions of In-111 CYT-103. Eight patients (3.5%) had reversible, nonserious adverse reactions, and 39% developed antimurine antibodies. Surgery revealed that 155 of 169 patients had colorectal carcinoma. In these 155 patients, immunoscintigraphy and CT demonstrated similar sensitivity (69% and 68%, respectively) and specificity (77%). However, immunoscintigraphy had greater sensitivity in detection of pelvic tumors (74% vs 57%, P = .035) and extrahepatic abdominal tumors (66% vs 34%, P less than .001); CT enabled detection of a greater proportion of liver metastases (84% vs 41%, P less than .001). These results indicate that In-111 CYT-103 can be administered safely and that immunoscintigraphy performed with this agent frequently enables identification of extrahepatic abdominal sites of disease not visualized with CT.

Adult↗

EphB2 as a therapeutic antibody drug target for the treatment of colorectal cancer.

Analysis of human colorectal cancer specimens revealed overexpression of the EphB2 receptor tyrosine kinase. Monoclonal antibodies (MAbs) to extracellular sequence of EphB2 were raised and tested for activity against colorectal cancer cells. One of the MAbs, 2H9, effectively blocked the interaction of ephB2 with ephrin ligands and inhibited the resulting autophosphorylation of the receptor. However, this antibody did not affect the proliferation of cancer cells expressing ephB2. Immunocytochemical analysis revealed rapid internalization of the MAb 2H9 on binding ephB2, suggesting that target-dependent cell killing could be achieved with an antibody-drug conjugate. When MAb 2H9 was conjugated to monomethylauristatin E through a cathepsin B-cleavable linker, it specifically killed ephB2-expressing cancer cells in vitro and in vivo. Our results suggest that ephB2 is an attractive target for immunoconjugate cancer therapy.

Adenocarcinoma↗

A phase I study of cantuzumab mertansine administered as a single intravenous infusion once weekly in patients with advanced solid tumors.

PURPOSE: The purpose is to determine the maximum-tolerated dose, assess the toxicities, characterize the pharmacokinetic behavior, and seek preliminary evidence of biological activity of cantuzumab mertansine when administered as a weekly i.v. infusion without interruption. EXPERIMENTAL DESIGN: Patients with incurable solid tumors that expressed the target antigen for cantuzumab mertansine, CanAg, were treated with doses of cantuzumab mertansine ranging from 40 to 138 mg/m(2). The maximum-tolerated dose was defined as the highest dose at which no more than 1 of 6 patients experienced dose-limiting toxicity. Plasma concentrations of cantuzumab mertansine and total humanized antibody were determined, and area under the plasma concentration-time curve (to the last measured concentration) was calculated. RESULTS: Thirty-nine patients received a total of 280 weekly doses of cantuzumab mertansine. Acute, transient elevation of the hepatic transaminases and reversible fatigue were identified as the dose-limiting toxicities at the highest dose level. The maximum-tolerated dose was determined to be 115 mg/m(2)/week. Evidence of clinical activity was noted in 3 patients. Pharmacokinetic analyses revealed that the pharmacokinetic variability was moderate, without evidence of dose dependency. Furthermore, the drug had a long terminal half-life ( approximately 40 h). CONCLUSIONS: This study identified a safe and tolerable dose of the novel immunoconjugate prodrug cantuzumab mertansine. The evidence of antitumor activity suggests that additional clinical development is warranted, with a focus on tumors that express high levels of CanAg and which are known to be sensitive to antimicrotubule agents.

Adult↗

Photochemical targeting of epidermal growth factor receptor: a mechanistic study.

PURPOSE: Photoimmunotherapy may allow target-specific photodynamic destruction of malignancies and may also potentiate anticancer antibody therapies. However, clinical use of either of the two modalities is limited for different reasons. Antibody therapies suffer from being primarily cytostatic and the need for prolonged administration with consequent side effects. In the case of photoimmunotherapy, a major impediment has been the absence of well-characterized photosensitizer immunoconjugates (PIC). In this investigation, we suggest a strategy to overcome these limitations and present the successful targeting of epidermal growth factor receptor (EGFR) using a well-characterized PIC. EXPERIMENTAL DESIGN: The PIC consisted of the EGFR-recognizing chimeric monoclonal antibody, C225, conjugated with a two-branched polyethylene glycol and benzoporphyrin derivative (BPD, Verteporfin). Mechanistic studies included photophysics, phototoxicity, cellular uptake, and catabolism experiments to yield dosimetric parameters. Target cells included two EGFR-overexpressing human cancer cell lines, OVCAR-5 and A-431. Nontarget cells included an EGFR-negative fibroblast cell line, 3T3-NR6, and a monocyte-macrophage cell line, J774. RESULTS: BPD-C225 PICs targeted and photodynamically killed EGFR-overexpressing cells, whereas free BPD exhibited no specificity. On a per mole basis, PICs were less phototoxic than free BPD, but PICs were very selective for target cells, whereas free BPD was not. Phototoxicity of the PICs increased at prolonged incubations. Photodynamic dose calculations indicated that PIC photophysics, photochemistry, catabolism, and subcellular localization were important determinants of PIC phototoxic potency. CONCLUSIONS: This study shows the efficacy of EGFR targeting with PIC constructs and suggests approaches to improve PIC designs and targeting strategies for in vivo photoimmunotherapy. The approach offers the possibility of dual effects via antibody-mediated cytostasis and photoimmunotherapy-based cytotoxicity.

Animals↗

EphB2 is a prognostic factor in colorectal cancer.

A receptor tyrosine kinase for ephrin ligands, EphB2 is expressed in colorectal cancer and has been proposed as a target for immunoconjugate therapy. The aim of this study was to perform a detailed histologic analysis of EphB2 expression in normal and neoplastic colorectal tissues. In addition, we sought to evaluate EphB2 expression as a prognostic factor in colorectal cancer. Expression of EphB2 was examined in normal colon (n = 28), colorectal cell lines (n = 20), colorectal adenomas (n = 148), primary cancers (n = 28), and metastases (n = 39) using immunohistochemistry. In addition, a series of primary cancers and matched normal (n = 342) with outcome data were profiled in tissue microarrays. The intensity of EphB2 expression was assessed in the entire series by immunohistochemistry, and in a subset by in situ hybridization. Overall survival and recurrence-free survival were correlated with EphB2 protein expression in retrospective subset analyses. Epithelial EphB2 expression was shown at all stages of colorectal tumorigenesis, including the base of all normal crypts, 77% of adenomas, 82% of primary cancers, and 64% of metastases. Although homogeneous expression was observed in adenomas, the pattern of staining was focal (mean 25%) in most malignant lesions. Patients whose tumor stained 2+ for EphB2 expression (versus 0/1+) exhibited significantly prolonged overall survival: mean duration of survival, 2,514 versus 1,044 days; hazard ratio, 0.45; 95% confidence interval, 0.18 to 0.95 (P = 0.035). In summary, EphB2 is expressed in normal crypts, colorectal adenomas, primary cancers, and metastases. High levels of EphB2 expression are associated with a longer mean duration of survival in colorectal cancer.

Adenoma↗